Relay stations (RSs) or Relay Nodes (RNs) have been proposed to extend coverage of a cellular system. Further, relay concepts may be utilized for                provisioning of high bit rate coverage in a shadowed environment;        reducing an average radio-transmission power at a user equipment (UE), thereby increasing the battery life of the UE;        enhancing a capacity of the cellular system as well as its effective throughput, e.g., increasing a cell-edge capacity and/or a balancing cell load;        enhancing an overall performance and deployment cost of a radio access network (RAN).        
FIG. 1 illustrates a typical deployment scenario of an LTE radio access network (RAN) comprising fixed relay nodes.
FIG. 1 shows a macro cell 109 comprising a base station or eNB 101, which is also referred to as a donor eNB (d-eNB). A UE 102 is directly served by the d-eNB 101. Furthermore, relay nodes 103, 104, 105 are served by the d-eNB 101 via backhaul links. A UE 106 is connected to the relay node 103, a UE 107 is connected to the relay node 104 and a UE 108 is connected to the relay node 105. The link between the UE 102, 106 to 108 and the d-eNB or the relay nodes 103 to 105 is also referred to as access link.
There are several kinds of relay systems. One example of a relay system comprises an amplifying and/or forwarding mechanism, e.g., applied in single frequency DVB-H networks.
Another example of a relay system utilizes a network coding scheme to improve the overall performance. A common relay type proposed for cellular relaying is a detect/forward type of relay, wherein an input signal is detected and retransmitted using the same procedure as in the original transmission.
Relaying can be realized at different layers of a protocol stack. An amplify-and-forward relaying scheme can be realized at a layer-1 of a protocol stack comprising (some part of) a physical (PHY) layer. Layer-2 relay nodes may include the protocol stack up to MAC/RLC layers, thereby enabling decentralized radio resource management. Layer-3 or higher layer relay nodes could be considered as wireless base stations and may support all protocol layers of a common base station. Such layer-3 relaying functionality may be referred to as type 1 relays pursuant to 3GPP.
In order to be economically viable, LTE-A is required to be as much backward compatible with Release 8 as possible. This is in particular crucial for the UE side, because then users may benefit from their Release 8 terminals being relayed. Hence, from a UE's viewpoint, a serving network node may advantageously function in the same way as does a Release 8 enhanced NodeB (eNB).
Based on such a requirement it may be difficult to reduce the capability or functionality of a relay node (compared to the base station, eNB) and at the same time still maintain full downward compatibility. Furthermore, relay nodes may have to support all main eNB functions. Hence, relay nodes may be capable of flexible resource sharing with a controlling eNB.
For example, at most two hops are allowed in the system, i.e. the eNB may directly serve the UE or it may serve the UE via a RN. In addition, a tree topology may be used, i.e. the RNs may not be connected with each other. These assumptions may be used in order to simplify the system setting. However, network topologies not employing these restrictions may be utilized as well.
A resource partitioning mechanism is required to coordinate radio resource usage within a macro cell between the d-eNB and the RNs. As the RN's transmitter causes interference to its own receiver, simultaneous d-eNB to RN and RN to UE transmissions on the same frequency resource may not be feasible unless sufficient isolation of the outgoing and incoming signals is provided, e.g., by means of specific, separated and/or isolated antenna structures.
Similarly, at the RN it may not be possible to receive UE transmissions simultaneously with the RN transmitting to the d-eNB. One possibility to handle the interference problem is to operate the RN such that it is not transmitting to UEs when it is supposed to receive data from the d-eNB, i.e. to create “gaps” in the resources used for transmitting data from the RN to the UE.
FIG. 2 shows a schematic diagram comprising several sub-frames visualizing an exemplary communication scheme. A sub-frame 201 comprising control information 202 and further data 203 is used for conveying data from a relay node to a UE. Another sub-frame 204 indicates a transmission gap, i.e. no data is conveyed between the relay node and the UE. Hence, this transmission gap can be used for d-eNB to relay node transmission purposes.
Such transmission gaps during which UEs (also Release 8 compliant UEs) are not supposed to expect any RN transmission can be created by configuring MBSFN sub-frames as also indicated in FIG. 2. Transmissions from the relay node to the d-eNB can be facilitated by not allowing any UE to RN transmissions in some sub-frames.
A centralized resource partitioning can be utilized, wherein the d-eNB assigns resources that each relay node connected to the d-eNB can utilize to serve its connected UEs. A user scheduling can be done at the relay nodes assuming, e.g., that only the resources assigned by the d-eNB are available.
FIG. 3 shows a schematic diagram depicting an example of a resource partitioning within a repetition window (or a resource partitioning window), wherein each relay node communicates with its connected UEs and with its d-eNB (in FIG. 3 referred to as “eNB”) in different sub-frames. The transmission between the d-eNB and its connected UEs can occur both within the sub-frame the relay node communicates with its UEs (if this is feasible due to an actual interference scenario) as well as within the sub-frame the relay node communicates with the d-eNB (not shown in FIG. 3).
In the Release 8 specification (e.g., 3GPP TS 36.423, Evolved Universal Terrestrial Radio Access Network (E-UTRAN); X2 Application Protocol (X2AP), V9.1.0, 2009-12) neighbor eNBs exchange the following load information messages to control inter-cell interference in uplink (UL) direction:    (a) An overload indication (OI) message indicates an interference level experienced by a sending eNB on each physical resource block (PRB) or group of PRBs. The OI is transmitted together with a source cell ID, i.e. the message contains the information about which cell is interfered. It is noted that one eNB can have multiple cells, therefore an indication of merely the eNB may not suffice and additional information may be provided for identification purposes.    (b) A high interference indication (HII) message indicates an occurrence of high interference sensitivity as perceived from a sending eNB on each PRB or group of PRBs. Hence, the HII message indicates where the sending eNB intends to schedule cell edge users. The HII message may be used to notify cell edge users resource usage so that neighbor cells can decide either not to schedule their users or only schedule center cell users on the resources advertised in the HII message. The HII message may be transmitted together with a target cell ID, i.e. it specifies from which cells a high interference could potentially affect the sending eNB. It is noted that an identification of the target eNB may not suffice, because it could have multiple cells. Hence, additional information may be provided for identification purposes.
These messages are used for inter-cell coordination between neighboring eNBs, but in the case of relaying, the interference co-ordination is basically carried out via resource partitioning.
The approach provided solves the problem as how to provide an efficient solution to support resource partitioning in particular in an LTE-A network utilizing at least one relay node.